The broad objective of this proposal is to elucidate the specific interactions between Porphyromonas gingivalis (P. gingivalis) and dendritic cells (DCs). P. gingivalis is a black pigmented, anaerobic, gram negative bacterium that is associated with most cases of chronic periodontitis (1). P. gingivalis expresses a myriad of virulence factors, most notably, fimbrial adhesins that enable it to bind to and invade host epithelial cells, endothelial cells, macrophages and DCs. While much is known about the 41 kDa major fimbria adhesin of P. gingivalis, the minor fimbriae have received little attention. Our data suggests that the minor fimbriae may serve as an immunosuppressive factor, by targeting the C-type lectin receptor DC-SIGN. DC- SIGN (CD209) is involved in uptake of pathogenic bacteria and certain viruses by DC (2-6), in the formation of DC-T cell conjugates, and is increasingly expressed in chronic periodontitis (CP) lesions. Targeting DC- SIGN for entry of DCs has proved an effective immuno-evasive strategy for certain pathogens;particularly those that cause chronic lifelong diseases such as tuberculosis and HIV. DC-SIGN ligation down-modulates NFKB-dependent maturation of DCs, dampens DC secretion of inflammatory and Thi-cytokines necessary for induction of protective immunity and, possibly, compromises intracellular killing mechanisms. The overall aim for this project is to investigate the role of the minor fimbriae of P. gingivalis in invasion of DCs and in activation of innate signaling pathways involved in immune suppression. The specific aims of this proposal therefore are: Aim 1: To determine receptor mediated internalization of P. gingivalis by monocyte derived dendritic cells (MoDCs). Aim 2: To purify the minor fimbriae and identify glycosylation motifs. Aim 3. To determine the role of minor fimbriae of P. gingivalis in modulation of MAPK signaling pathways involved in cytokine secretion and maturation of MoDC. Overall, these studies will identify the role ofthe minor fimbrial adhesin of P. gingivalis in: (i) entry of DCs and intracellular routing and survival, and (ii) activation of intracellular signaling pathways responsible for immuno-suppression by P. gingivalis. Moreover, the identification of lectin binding carbohydrate motifs on minor fimbriae and the generation of monoclonal antibodies against the purified fimbriae will be invaluable for structure-function studies and will advance the field of mucosal pathogenesis.